Coated narrow band red phosphor

ABSTRACT

A coated phosphor comprises: phosphor particles comprised of a phosphor with composition MSe 1−x S x :Eu, wherein M is at least one of Mg, Ca, Sr, Ba and Zn and 0&lt;x&lt;1.0; and a coating on individual ones of the phosphor particles, the coating comprising a layer of oxide material encapsulating the individual phosphor particles; wherein the coated phosphor is configured such that under excitation by a blue LED the reduction in photoluminescent intensity at the peak emission wavelength after 1,000 hours of aging at about 85° C. and about 85% relative humidity is no greater than about 15%; and wherein the coated phosphor is configured such that the change in chromaticity coordinates CIE(x), Δx, after 1,000 hours of aging at about 85° C. and about 85% relative humidity is less than or equal to about 5×10 −3 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Pat. No. 10,253,257, issuedApr. 9, 2019, which in turn claims the benefit of priority to U.S.Provisional Application No. 62/260,230, filed Nov. 25, 2015, both ofwhich are hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

Embodiments of the present invention are directed to coated narrow bandred phosphors with general composition MSe_(1−x)S_(x):Eu, wherein M isat least one of Mg, Ca, Sr, Ba and Zn and 0<x<1.0 and the coating is anoxide chosen from the group of materials consisting of aluminum oxide,silicon oxide, titanium oxide, zinc oxide, magnesium oxide, zirconiumoxide and chromium oxide, and light emitting devices including the same.

BACKGROUND OF THE INVENTION

Warm white light emitting diodes (LEDs) with high-color-rendering index(CRI, Ra>80) and low correlated color temperature (CCT<4500K) need asuitable red phosphor. Successful phosphor materials include materialssuch as Eu²⁺ or Ce³⁺ doped (oxy)nitride compounds, for example(Ba,Sr)₂Si₅N₈:Eu²⁺ and (Ca,Sr)AlSiN₃:Eu²⁺. However, these phosphors havedrawbacks when used in certain applications since their emission spectraare broad (full-width at half maximum is approximately 75-85 nm) and alarge part of the spectrum is beyond 650 nm in wavelength—a part of thespectrum to which human eyes are insensitive—which significantly reducesthe lumen efficacy of LED lighting. MSe_(1−x)S_(x):Eu materials show redcolor emission from 600 to 650 nm, and provide high lumen efficacy ofLED lighting after combining with yellow or green phosphors. However,the narrow band red phosphors with general composition MSe_(1−x)S_(x):Euare hygroscopic, and exhibit rapid deterioration of photoluminescencedue to exposure to moisture (water vapor), oxygen and/or heat. Clearlythere is a need for narrow band red phosphors with general compositionMSe_(1−x)S_(x):Eu, with coatings which are effective at protecting thephosphor particles from moisture and oxygen and enable a commerciallyuseful phosphor.

SUMMARY OF THE INVENTION

A coated phosphor may in some embodiments comprise: phosphor particles,wherein the phosphor particles are comprised of a phosphor withcomposition MSe_(1−x)S_(x):Eu, wherein M is at least one of Mg, Ca, Sr,Ba and Zn and 0<x<1.0; and a coating on individual ones of the phosphorparticles, the coating comprising a layer of oxide materialencapsulating the individual phosphor particles; wherein the coatedphosphor is configured such that under excitation by a blue LED thereduction in photoluminescent intensity at the peak emission wavelengthafter 1,000 hours of aging at about 85° C. and about 85% relativehumidity (RH) is no greater than about 15%; and wherein the coatedphosphor is configured such that the change in chromaticity coordinatesCIE(x), Δx, after 1,000 hours of aging at about 85° C. and about 85%relative humidity is less than or equal to about 10×10⁻³.

In some embodiments, a coated phosphor may comprise: phosphor particles,wherein the phosphor particles are comprised of a phosphor withcomposition MSe_(1−x)S_(x):Eu, wherein M is at least one of Mg, Ca, Sr,Ba and Zn and 0<x<1.0; and a coating on individual ones of the phosphorparticles, comprising a layer of oxide material encapsulating theindividual phosphor particles; wherein the coated phosphor is configuredsuch that the coated phosphor does not turn black when suspended in a 1mol/L silver nitrate solution for at least 5 days at 20° C. Inembodiments, the coated phosphor is configured such that the coatedphosphor does not turn black when suspended in a 1 mol/L silver nitratesolution for at least 2 hours at 85° C.

In some embodiments, a method of forming a coated phosphor may comprise:providing phosphor particles, wherein the phosphor particles arecomprised of a phosphor with composition MSe_(1−x)S_(x):Eu, wherein M isat least one of Mg, Ca, Sr, Ba and Zn and 0<x<1.0; and depositing acoating on individual ones of the phosphor particles by a gas phaseprocess in a fluidized bed reactor, the coating comprising a layer ofoxide material encapsulating the individual phosphor particles; whereinthe coated phosphor is configured to satisfy one or more of theconditions: (1) such that under excitation by a blue LED the reductionin photoluminescent intensity at the peak emission wavelength after1,000 hours of aging at about 85° C. and about 85% relative humidity isno greater than about 15%; (2) such that the change in chromaticitycoordinates CIE(x), Δx, after 1,000 hours of aging at about 85° C. andabout 85% relative humidity is less than or equal to about 10×10⁻³; and(3) wherein the coated phosphor is configured such that the coatedphosphor does not turn black when suspended in a 1 mol/L silver nitratesolution for at least 2 hours at 85° C.

In some embodiments, a white light emitting device comprising: anexcitation source with emission wavelength within a range from 200 nm to480 nm; a coated phosphor according to any of the embodiments describedherein, with a first phosphor peak emission wavelength; and a secondphosphor with a second phosphor peak emission wavelength different tosaid first phosphor peak wavelength.

In some embodiments, a white light emission device for backlighting,comprising: an excitation source with emission wavelength within a rangefrom 440 nm to 480 nm; a coated phosphor according to any of theembodiments described herein, with a first phosphor peak emissionwavelength between about 625 nm and about 645 nm; and a second phosphorwith a second phosphor peak emission wavelength different to said firstphosphor peak wavelength, said second phosphor peak emission wavelengthbeing between about 520 nm and about 545 nm; wherein said white lightemission device has an emission spectrum with clearly separated blue,green and red peaks, and a color gamut after liquid crystal display(LCD) red, green and blue (RGB) color filters of at least 85% of theNTSC (National Television System Committee) standard.

In some embodiments, a white light emission device may comprise: anexcitation source with emission wavelength within a range from 200 nm to480 nm; and a remote phosphor component comprising green-yellowphosphors with a peak emission wavelength between about 500 nm and about600 nm and a coated phosphor according to any of the embodimentsdescribed herein with a peak emission wavelength between about 600 nmand about 650 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects and features of the present invention willbecome apparent to those ordinarily skilled in the art upon review ofthe following description of specific embodiments of the invention inconjunction with the accompanying figures, wherein:

FIG. 1 shows normalized emission spectra of CSS (CaSe_(1−x)S_(x):Eu)phosphors for differing ratios of S/Se;

FIG. 2 is a schematic representation of a phosphor particle coatingapparatus according to an embodiment of the invention;

FIGS. 3A and 3B are SEM micrographs of coated CSS phosphor particlesaccording to an embodiment of the invention;

FIG. 4A is a TEM micrograph of a portion of a coated CSS phosphorparticle according to some embodiments;

FIGS. 4B-4E are electron diffraction patterns for various regions ofFIG. 4A denoted Areas 1-4;

FIG. 5 shows reliability data, relative photoluminescence intensityversus time, for an LED operated under accelerated testing conditions85° C./85% RH for i) uncoated CSS, ii) coated CSS according to anembodiment of the invention and iii) red nitride phosphors;

FIG. 6 shows reliability data, change of chromaticity Δ CIE x versustime, for an LED operated under accelerated testing conditions 85°C./85% RH for i) uncoated CSS, ii) coated CSS according to an embodimentof the invention and iii) red nitride phosphors;

FIG. 7 shows % retained brightness versus time for a coated prior artZnS phosphor;

FIG. 8 shows reliability data, relative photoluminescence intensityversus time, for an LED operated under accelerated testing conditions85° C./85% RH for (i) a first blue LED#1 combined with a red nitridephosphor, (ii) a first blue LED#1 combined with coated CSS phosphoraccording to some embodiments and (iii) a second blue LED#2 combinedwith coated CSS phosphor according to some embodiments;

FIG. 9 shows reliability data, change of chromaticity Δ CIE x versustime, for an LED operated under accelerated testing conditions 85°C./85% RH for (i) a first blue LED#1 combined with a red nitridephosphor, (ii) a second blue LED#2 combined with a red nitride phosphor,(iii) a first blue LED#1 combined with coated CSS phosphor according tosome embodiments and (iv) a second blue LED#2 combined with coated CSSphosphor according to some embodiments;

FIG. 10 is a schematic representation of shows a white light emittingdevice, according to some embodiments;

FIG. 11 white light emission spectra of a blue LED combined with (i) ared nitride phosphor and a green aluminate phosphor and (ii) a coatedCSS phosphor and a green aluminate phosphor, according to someembodiments;

FIG. 12 shows reliability data, relative photoluminescence intensityversus time, for a white light emitting device operated underaccelerated testing conditions 85° C./85% RH for a blue LED combinedwith a coated CSS phosphor and a green aluminate phosphor, according tosome embodiments;

FIG. 13 shows reliability data, change of chromaticity Δ CIE x versustime, for a white light emitting device operated under acceleratedtesting conditions 85° C./85% RH for a blue LED combined with a coatedCSS phosphor and a green aluminate phosphor, according to someembodiments;

FIGS. 14A & 14B show a white light remote phosphor solid-state lightemitting device, according to some embodiments;

FIG. 15 white light emission spectra of a remote phosphor light emittingdevice with a remote phosphor wavelength conversion component comprisingcoated CSS phosphor and a green aluminate phosphor, according to someembodiments;

FIG. 16 shows reliability data, relative photoluminescence intensityversus time, for a white light remote phosphor light emitting devicewith a remote phosphor wavelength conversion component comprising coatedCSS phosphor and a green aluminate phosphor, according to someembodiments for (i) Disc 1 operated under accelerated testing conditions85° C./85% RH, (ii); Disc 2 operated under accelerated testingconditions 85° C./85% RH, and (iii) Disc 3 operated under roomtemperature conditions;

FIG. 17 shows reliability data, change of chromaticity Δ CIE x versustime, for a white light remote phosphor light emitting device with aremote phosphor wavelength conversion component comprising coated CSSphosphor and a green aluminate phosphor, according to some embodimentsfor (i) Disc 1 operated under accelerated testing conditions 85° C./85%RH, (ii); Disc 2 operated under accelerated testing conditions 85°C./85% RH, and (iii) Disc 3 operated under room temperature conditions;

FIG. 18 shows reliability data, relative photoluminescence intensityversus time, for a white light remote phosphor light emitting devicewith a remote phosphor wavelength conversion component comprising coatedCSS phosphor and a green aluminate phosphor, according to someembodiments for (i) Disc 1 stored under accelerated testing conditions85° C./85% RH, and (ii) Disc 2 stored under accelerated testingconditions 85° C./85% RH;

FIG. 19 shows reliability data, change of chromaticity Δ CIE x versustime, for a white light remote phosphor light emitting device with aremote phosphor wavelength conversion component comprising coated CSSphosphor and a green aluminate phosphor, according to some embodimentsfor (i) Disc 1 stored under accelerated testing conditions 85° C./85%RH, and (ii) Disc 2 stored under accelerated testing conditions 85°C./85% RH;

FIG. 20 shows the filtering characteristics, light transmission versuswavelength, for red, green and blue filter elements of an LCD display;

FIG. 21 white light emission spectra of a white light emitting devicecomprising coated CSS phosphor and a β-SiAlON (540 nm) phosphor,according to some embodiments and the emission spectrum after filtering;and

FIG. 22 shows the 1931 CIE color coordinates of the NTSC standard andthe calculated RGB color coordinates from the white light source forwhich a spectrum is shown in FIG. 21, according to some embodiments.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the present invention will now be described in detailwith reference to the drawings, which are provided as illustrativeexamples of the invention so as to enable those skilled in the art topractice the invention. Notably, the figures and examples below are notmeant to limit the scope of the present invention to a singleembodiment, but other embodiments are possible by way of interchange ofsome or all of the described or illustrated elements. Moreover, wherecertain elements of the present invention can be partially or fullyimplemented using known components, only those portions of such knowncomponents that are necessary for an understanding of the presentinvention will be described, and detailed descriptions of other portionsof such known components will be omitted so as not to obscure theinvention. In the present specification, an embodiment showing asingular component should not be considered limiting; rather, theinvention is intended to encompass other embodiments including aplurality of the same component, and vice-versa, unless explicitlystated otherwise herein. Moreover, applicants do not intend for any termin the specification or claims to be ascribed an uncommon or specialmeaning unless explicitly set forth as such. Further, the presentinvention encompasses present and future known equivalents to the knowncomponents referred to herein by way of illustration.

FIG. 1 shows normalized emission spectra of CSS (CaSe_(1−x)S_(x):Eu)phosphors for differing ratios of S/Se, the emission peak can be tunedfrom 600 nm to 650 nm by the ratio of S/Se in the composition andexhibits a narrow band red emission spectrum with full width halfmaximum (FWHM) typically in the range from ˜48 nm to ˜60 nm (longerwavelength typically has a larger FWHM value), when excited by a bluelight source with a peak emission of about 450 nm. For comparison, aCASN red nitride phosphor (a calcium aluminum silicon nitride basedphosphor) typically has a FWHM of ˜80 nm. Note that x varies from about0.05 to about 0.8 for the compositions shown in FIG. 1—the higher peakwavelengths corresponding to the larger values of x.

CSS particles are synthesized from purified CaSeO₄ and CaSO₄ in a mildH₂ (gas) environment (for example ˜5% H₂/N₂). Herein, unless otherwisespecified, CSS phosphor samples used in the examples have a compositionof CaSe_(1−x)S_(x):Eu with x ˜0.2. The particles are coated by a CVDprocess in a fluidized bed reactor. FIG. 2 is a schematic representationof a phosphor particle coating apparatus according to an embodiment ofthe invention. Reactor 20 comprises a porous support disc 22, over whichphosphor powder 24 is held, and inlets 26 and 28 for metal organicprecursor and water vapor, respectively. The coating materials may beone or more materials chosen from the group consisting of aluminumoxide, silicon oxide, titanium oxide, zinc oxide, magnesium oxide,zirconium oxide and chromium oxide. The thickness may typically be inthe range of 100 nanometers to 5 microns, in embodiments in the range of50 nm to 100 nm, 100 nm to 500 nm, 500 nm to 1 um, or 1 um to 2 um.Herein, unless otherwise specified, coated CSS samples used in theexamples herein are coated with approximately 1 micron of alumina.

In a typical coating process, the phosphor powder sample was loaded intothe reactor and heated to 100-250° C., preferably 200° C., under N₂ gasflow. A metal oxide precursor such as TrimethylAluminum (TMA), Titaniumtetra-chloride (TiCl₄), Silicon tetra-chloride (SiCl₄), or DimethylZincwas introduced in to the reactor with a N₂ carrier gas through abubbler. H₂O vapor was also introduced into the reactor to react withthe metal oxide precursor to form oxide coating layers on phosphorparticles. Complete fluidization of the particles being coated (from gasflow optimization, etc.) without any dead space is important to ensurehomogeneous coating of all phosphor particles. In a typical coatingconducted at 200° C., for a 250 g phosphor particle loading of thereactor, the coating was produced with a metal oxide precursor feedingrate of 1 to 10 g/hour for 4 hours, while feeding H₂O at a rate of 2 to7 g/hour. It is shown below that these conditions can produce dense andpinhole free coatings and the present inventors expect that theseconditions are required to produce dense substantially pin-hole freecoatings of uniform thickness, with theorized bulk density for thecoatings of greater than 95% and in embodiments greater than 99%. It isexpected by the present inventors that outside of: the specified feedingrate range for oxide precursor, the specified feeding rate range forH₂O, and/or the specified 100-250° C. temperature range, the coatedphosphors will not exhibit the reliability documented herein.

The coated CSS phosphor particles were tested using an Ocean OpticsUSB4000 spectrometer for photoluminescence intensity (PL) andchromaticity (CIE coordinates x and y). It was found that there is nosignificant peak emission position or color (CIE) change after coatingthe CSS particles. The PL (relative photo luminance intensity) is alsonot reduced after coating but actually increased which results in abrightness increase compared to the uncoated sample as shown in Table 1.

TABLE 1 Typical photo-luminance property of CSS phosphor before andafter coating Sample PL PE (nm) CIE x Brightness (%) Before Coating 100%614.5 0.646 100 After Coating 111% 614.9 0.648 103.3

FIGS. 3A and 3B are SEM micrographs of coated CSS phosphor particlesaccording to an embodiment of the invention; the sample shows CSSparticles 30, with coating 32, embedded in epoxy 34. The samples wereprepared by dispersing the phosphor particles in epoxy then curing.After curing, the epoxy (with CSS powder) was polished and then coveredby a flash of sputtered Pd—Au metal to enhance the sample's electronicconductivity (the metal reduces/removes electron charging when analyzingthe sample in the SEM). The prepared cross section sample was thenanalyzed by scanning electron microscopy (SEM) which clearly showed thehermetic coating layer of alumina around the CSS particles (completecoverage by coating layer of particle without observable gaps orpinholes), as shown in FIGS. 3A & 3B. Diameters of the phosphorparticles are in a range between 5 microns and 20 microns.

FIG. 4A is a TEM micrograph of a portion of a coated CSS phosphorparticle according to some embodiments; a thin section sample of thecoated CSS phosphor particles was also analyzed in a TEM to reveal thefine structure of the coating layer which showed a dense amorphous oxidecoating layer on the CSS particle surface without pinholes. FIGS. 4B-4Eare electron diffraction patterns for various regions of FIG. 4A denotedas Areas 1 through 4, showing the amorphous structure of the coating(Areas 1-3) and the crystalline structure of the CSS particle (Area 4).

The stability and reliability of the coated CSS phosphor particles maybe established using a silver test, as follows. Silver ions (Ag⁺) canattack S/Se in CSS to form a black Ag₂S/Ag₂Se compound if the CSSsurface is not well protected (for example, if pinholes are present inthe coating black Ag₂S/Ag₂Se spots would form). The silver test is basedon this mechanism and involves soaking the coated CSS materials in AgNO₃solution to evaluate how well the coating layer is able to protect theCSS phosphor particle against Ag⁺ attack. The longer the time the CSScan survive in the Ag test, the better the surface protection(coating/reliability) the phosphor should have.

In a Ag test, CSS powder was soaked in 1 mol/L AgNO₃ solution, and thestability of the sample was evaluated by monitoring how long the powdercan survive without turning black. For comparison, it is noted thatuncoated CSS samples turn black in as little as 1 minute. Test resultsshow that a well coated sample can survive without blackening for morethan 30 days.

FIG. 5 shows reliability data, relative photoluminescence intensityversus time, for an LED operated under accelerated testing conditions85° C./85% RH for i) uncoated CSS, ii) coated CSS according to anembodiment of the invention and iii) red nitride phosphors. The LEDpackage with uncoated CSS phosphor failed within ˜48 hours under 350 mAat 85° C./85% RH—the brightness dropped ˜25% in 24 hours and dropped 60%after 100 h. FIG. 6 shows reliability data, change of chromaticity Δ CIEx versus time, for an LED operated under accelerated testing conditions85° C./85% RH for i) uncoated CSS, ii) coated CSS according to anembodiment of the invention and iii) red nitride phosphors; CIE xchanged 0.06 after 100 hours for the uncoated CSS. CSS with optimizedcoating according to embodiments passed 1000 hours 85° C./85% RHreliability test with brightness drop of less than 10% and CIE x changewithin 0.005, with a similar performance to the red nitride (CASN)reference.

FIG. 7 shows % retained brightness versus time for a prior art coatedZnS phosphor—FIG. 4 from U.S. Pat. No. 5,418,062—which lost 20%brightness in 175 hours at room temperature. In FIG. 7, 56 is anuncoated phosphor tested in a dry environment, 54 is an uncoatedphosphor tested in a >95% RH environment, 66 is a coated phosphor testedin a >95% RH environment, and 64 is a coated phosphor tested in a dryenvironment. The coating process of the '062 patent is not as effectiveas the coating process of the present invention.

The problem for sulfide materials used to coat LEDs that have Ag-coatedlead frame is that the sulfide in the phosphor may react with thesilver. To evaluate this potential problem, coated CSS phosphor of thepresent invention were tested on two different LEDs with Ag-coated leadframes. (LED#1 is a Lextar 3030 LED—3.0 mm×3.0 mm lead frame packagewith silver electrodes. LED#2 is a Jufei 7020 LED—7.0 mm×2.0 mm leadframe package with silver electrodes.) FIGS. 8 & 9 show the coated CSShas the same stable reliability performance as a red nitride (CASN)reference, and it clearly demonstrates the hermetic encapsulation of thecoated CSS phosphor of the present invention. FIG. 8 shows reliabilitydata, relative photoluminescence intensity versus time, for an LEDoperated under accelerated testing conditions 85° C./85% RH for (i) afirst blue LED#1 combined with a red nitride phosphor, (ii) a first blueLED#1 combined with coated CSS phosphor according to some embodimentsand (iii) a second blue LED#2 combined with coated CSS phosphoraccording to some embodiments. FIG. 9 shows reliability data, change ofchromaticity Δ CIE x versus time, for an LED operated under acceleratedtesting conditions 85° C./85% RH for (i) a first blue LED#1 combinedwith a red nitride phosphor, (ii) a second blue LED#2 combined with ared nitride phosphor, (iii) a first blue LED#1 combined with coated CSSphosphor according to some embodiments and (iv) a second blue LED#2combined with coated CSS phosphor according to some embodiments.

Packaged White Light Emitting Device, for Display Backlight and GeneralLighting Device

FIG. 10 illustrates a white light emitting device, according to someembodiments. The device 1000 can comprise a blue light emitting, withinthe range of 450 nm to 470 nm, GaN (gallium nitride) LED chip 1002 forexample, housed within a package. The package, which can for examplecomprise a low temperature co-fired ceramic (LTCC) or high temperaturepolymer, comprises upper and lower body parts 1004, 1006. The upper bodypart 1004 defines a recess 1008, often circular in shape, which isconfigured to receive the LED chips 1002. The package further compriseselectrical connectors 1010 and 1012 that also define correspondingelectrode contact pads 1014 and 1016 on the floor of the recess 1008.Using adhesive or solder, the LED chip 1002 can be mounted to athermally conductive pad 1018 located on the floor of the recess 1008.The LED chip's electrode pads are electrically connected tocorresponding electrode contact pads 1014 and 1016 on the floor of thepackage using bond wires 1020 and 1022 and the recess 1008 is completelyfilled with a transparent polymer material 1024, typically a silicone,which is loaded with a mixture of a red emitting phosphor material ofthe present invention and a second phosphor with a second phosphor peakemission wavelength different from the red emitting phosphor peakwavelength such that the exposed surfaces of the LED chip 1002 arecovered by the phosphor/polymer material mixture. To enhance theemission brightness of the device the walls of the recess are inclinedand have a light reflective surface. In some embodiments, the secondphosphor is a green emitting phosphor, and in other embodiments thesecond phosphor is a green or yellow-emitting phosphor having a peakemission wavelength between about 515 nm and about 570 nm.

Due to its narrow band emission spectrum, CSS phosphor shows betterbrightness performance than CASN red nitride phosphor. Table 2 shows for2700K 90CRI, that CSS is 18.6% brighter than CASN red nitride with CRIover 90; the white LED spectrum for the two phosphors is shown forcomparison in FIG. 11.

TABLE 2 CSS phosphor + green phosphor (535 nm) for 2700K 90 CRI lightingFlux Bright- Sample (lm) ness CIE x CIE y CCT CRI R9 CASN red 7.240100.0% 0.4600 0.4104 2697K 91.0 56.5 nitride (~645 nm) CSS 8.590 118.6%0.4599 0.4107 2700K 90.4 27.5 (~625 nm)

FIG. 11 shows white light emission spectra of a blue LED combined with(i) a red nitride phosphor and a green aluminate phosphor and (ii) acoated CSS phosphor and a green aluminate phosphor, according to someembodiments. The green phosphor is an aluminate phosphor, GAL535,available from Intematix Corp.

Coated CSS of the present invention was blended with green aluminatephosphor (GAL535) to achieve warm white (CCT 3000K) luminance in aceramic high power LED package. The package was tested at 350 mA, 85°C./85% RH for life reliability. FIG. 12 shows reliability data, relativephotoluminescence intensity versus time, for a white light emittingdevice operated under accelerated testing conditions 85° C./85% RH for ablue LED combined with a coated CSS phosphor and a green aluminatephosphor, according to some embodiments. FIG. 13 shows reliability data,change of chromaticity Δ CIE x versus time, for a white light emittingdevice operated under accelerated testing conditions 85° C./85% RH for ablue LED combined with a coated CSS phosphor and a green aluminatephosphor, according to some embodiments. The figures show the brightnessand CIE of the white LED package are very stable—showing almost nochange during the reliability test.

Remote Phosphor White Light Emitting Device

FIGS. 14A and 14B illustrate a remote phosphor solid-state white lightemitting device, according to some embodiments. The device 1400 isconfigured to generate warm white light with a CCT (Correlated ColorTemperature) of 2700K and a CRI (Color Rendering Index) of about 90. Thedevice can be used as a part of a downlight or other lighting fixture.The device 1400 comprises a hollow cylindrical body 1402 composed of acircular disc-shaped base 1404, a hollow cylindrical wall portion 1406and a detachable annular top 1408. To aid in the dissipation of heat,the base 1404 is preferably fabricated from aluminum, an alloy ofaluminum or any material with a high thermal conductivity. The base 1404can be attached to the wall portion 1406 by screws or bolts or by otherfasteners or by means of an adhesive.

The device 1400 further comprises a plurality (four in the exampleillustrated) of blue light emitting LEDs 1412 (blue LEDs) that aremounted in thermal communication with a circular-shaped MCPCB (metalcore printed circuit board) 1414. The blue LEDs 1412 can comprise aceramic packaged array of twelve 0.4 W GaN-based (gallium nitride-based)blue LED chips that are configured as a rectangular array 3 rows by 4columns. To maximize the emission of light, the device 1400 can furthercomprise light reflective surfaces 1416 and 1418 that respectively coverthe face of the MCPCB 1414 and the inner curved surface of the top 1408.

The device 1400 further comprises a photoluminescent wavelengthconversion component 1420 that is located remotely to the LEDs andoperable to absorb a proportion of the blue light generated by the LEDs1412 and convert it to light of a different wavelength by a process ofphotoluminescence. The emission product of the device 1400 comprises thecombined light generated by the LEDs 1412 and the photoluminescentwavelength conversion component 1420. The photoluminescent wavelengthconversion component may be formed of a light transmissive material (forexample, polycarbonate, acrylic material, silicone material, etc.) andcomprises a mixture of a yellow, red and/or green phosphor, including(coated) red phosphor material of the present invention. Furthermore, inembodiments the photoluminescent wavelength conversion component may beformed of a light transmissive material coated with phosphor material asdescribed above, including (coated) red phosphor material of the presentinvention. The wavelength conversion component is positioned remotely tothe LEDs 1412 and is spatially separated from the LEDs. In this patentspecification “remotely” and “remote” means in a spaced or separatedrelationship. The wavelength conversion component 1420 is configured tocompletely cover the housing opening such that all light emitted by thelamp passes through the component 1420. As shown the wavelengthconversion component 1420 can be detachably mounted to the top of thewall portion 1406 using the top 1408 enabling the component and emissioncolor of the lamp to be readily changed.

In addition to applications in LED packages for lighting, CSS can alsobe used in a remote phosphor mode. CSS was used with GAL535 in a remotephosphor disk with CCT 4000K 90CRI. Compared with red nitride in thesame remote phosphor disk, CSS materials showed ˜11% brightnessimprovement and similar thermal quenching performance. At 80° C. bothred nitride and CSS have a CE drop of ˜5% compared to performance at 28°C. and the CSS still exhibits roughly 11% higher brightness than the rednitride reference (as Table 3 shows). FIG. 15 shows a typical whitelight emission spectra of a remote phosphor light emitting device with aremote phosphor wavelength conversion component comprising coated CSSphosphor and a green aluminate phosphor, according to some embodiments;the green phosphor is an aluminate phosphor, GAL535, available fromIntematix Corp.

TABLE 3 CSS performance compared to red nitride in remote phosphor modeTemp. CCT CRI Flux CE CE LE LE Sample (° C.) CIE x CIE y (K) Ra (lm)(lm/BW) (%) (lm/W) (%) CASN 28.3 0.3851 0.3868 3951 88.8 1766 197.5 100300.9 100 Red nitride CSS 28.5 0.3822 0.3866 4024 89.6 1966 219.8 111338.0 112 CASN 80 0.3821 0.3792 3970 91.1 1674 188.2 95 295.1 98 Rednitride CSS 80 0.3735 0.3842 4241 87.6 1863 208.4 106 337.4 112

In remote phosphor applications, CSS materials (coated) also showexcellent reliability performance, flat trend over 2000 hours inoperation mode well within control limits for both brightness (greaterthan 90%) and color (CIE) changes (within +/−0.005) (FIGS. 16 & 17), andfor storage over 3000 hours also shows a flat trend well within the samecontrol limits (FIGS. 18 & 19). FIG. 16 shows reliability data, relativephotoluminescence intensity versus time, for a white light remotephosphor light emitting device with a remote phosphor wavelengthconversion component comprising coated CSS phosphor and a greenaluminate phosphor, according to some embodiments for (i) Disc 1operated under accelerated testing conditions 85° C./85% RH, (ii) Disc 2operated under accelerated testing conditions 85° C./85% RH, and (iii)Disc 3 stored and operated under room temperature conditions—provided asa reference. FIG. 17 shows reliability data, change of chromaticity ΔCIE x versus time, for a white light remote phosphor light emittingdevice with a remote phosphor wavelength conversion component comprisingcoated CSS phosphor and a green aluminate phosphor, according to someembodiments for (i) Disc 1 operated under accelerated testing conditions85° C./85% RH, (ii) Disc 2 operated under accelerated testing conditions85° C./85% RH, and (iii) Disc 3 stored and operated under roomtemperature conditions—provided as a reference. FIG. 18 showsreliability data, relative photoluminescence intensity versus time, fora white light remote phosphor light emitting device with a remotephosphor wavelength conversion component comprising coated CSS phosphorand a green aluminate phosphor, according to some embodiments for (i)Disc 1 stored under accelerated testing conditions 85° C./85% RH, and(ii) Disc 2 stored under accelerated testing conditions 85° C./85% RH.FIG. 19 shows reliability data, change of chromaticity Δ CIE x versustime, for a white light remote phosphor light emitting device with aremote phosphor wavelength conversion component comprising coated CSSphosphor and a green aluminate phosphor, according to some embodimentsfor (i) Disc 1 stored under accelerated testing conditions 85° C./85%RH, and (ii) Disc 2 stored under accelerated testing conditions 85°C./85% RH.

In addition to its applications in general LED lighting applications,due to its narrow band red and suitable wavelength, CSS phosphors canalso be used in back lighting. FIG. 20 shows the filteringcharacteristics, light transmission versus wavelength, for red, greenand blue filter elements of an LCD display. FIG. 21 shows coated CSSphosphor particles, according to some embodiments, with β-SiAlON (540nm) before and after filtering, which shows separation of blue, greenand red peaks. Table 4 shows, when used with β-SiAlON (540 nm), redcoated CSS phosphor with an emission wavelength of about 627 nm canachieve 88% of the area of the NTSC standard. Furthermore, theperformance against the NTSC standard was found to increase withincreasing emission wavelength of the red coated CSS phosphor. Note thatthe LCD white measurements are for an LCD operating to produce a whitescreen and using a backlight LED according to embodiments, and the LCDred/green/blue filter measurements are for light from the LCD whichcomes only through the particular color filter—red, green or blue.

TABLE 4 CSS + β-SiAlON540 used for backlighting Parameter ValueBacklight LED CIE x 0.280 Backlight LED CIE y 0.260 Backlight LEDBrightness (lm) 21.008 LCD white CIE x 0.318 LCD white CIE y 0.343 LCDBrightness (lm) 16.08 Brightness LCD/LED (%) 76.5 Red CIE x after LCDred filter 0.664 Red CIE y after LCD red filter 0.336 Green CIE x afterLCD green filter 0.285 Green CIE y after LCD green filter 0.659 Blue CIEx after LCD blue filter 0.157 Blue CIE y after LCD blue filter 0.032NTSC (%) 88.2

White LEDs using combined blue LED and YAG:Ce phosphor have been widelyused as backlights for personal computer LCD screens, LCD TVs andsmall-sized LCDs used in devices such as cellular phones and tabletdisplays. To date, the color gamut of these LEDs can attainapproximately 70% of the area of the NTSC standard, and the widest colorgamut using a narrow-band β-SiAlON:Eu green phosphor and CaAlSiN₃:Eu redphosphor can reach ˜85% of the area of the NTSC standard with theassistance of typical LCD color filters. Cd-based green and red quantumdots (QDs) have reached a wider color gamut—more than 115% of the areaof the NTSC standard in the 1931 CIE xy color space; however, Cd-basedQDs are toxic and environmentally harmful. The widest color gamut thatCd-free QDs, such as InP/ZnS QDs, can reach is approximately 87%relative to the NTSC standard. However, the combination of a red coatedCSS phosphor, as described herein, with an emission wavelength of about627 nm, with various narrow band green phosphors, such as β-SiAlON:Eu orSrGa₂S₄:Eu, can reach approximately 88% of the area of the NTSCstandard. See FIG. 22 which shows the 1931 CIE color coordinates of theNTSC standard (callout 2210) and the calculated RGB coordinates from awhite light source comprising a blue LED (451 nm) combined with the redcoated CSS phosphor of the present invention with the green phosphorβ-SiAlON:Eu (540 nm) (callout 2220); this is the same white light sourcefor which a spectrum is shown in FIG. 21 and described above in Table 4.Note that herein references to the percentage of the area of the NTSCstandard are percentages of the area of the NTSC (National TelevisionSystem Committee) 1953 color gamut specification as mapped on the CIE1931 xy chromaticity diagram. Furthermore, when the wavelength of thered coated CSS phosphor, as described herein, with an emissionwavelength of about 635 nm in combination with green phosphor such asβ-SiAlON:Eu or SrGa₂S₄:Eu, can reach more than 93% of the area of theNTSC standard.

It is expected that some embodiments of the coated narrow band red CSSphosphors of the present invention when combined with one of the variouspossible narrow band green phosphors such as β-SiAlON:Eu, SrGa₂S₄:Eu orInP/ZnS green quantum dots are able to reach high efficiencies and highlevels of color gamut for LED backlight applications, where thephosphors are integrated into “on-chip”, “on-edge” or “on-film” LEDbacklights. Furthermore, it is expected that the performance of someembodiments of the coated narrow band red phosphors of the presentinvention in combination with one of the various possible narrow bandgreen phosphors will provide higher efficiencies and higher levels ofcolor gamut compared with red nitride phosphors such as(Ba,Sr)₂Si₅N₈:Eu²⁺ or (Ca,Sr)AlSiN₃:Eu²⁺ in combination with the samenarrow band green phosphors.

Although examples of the present invention have been described withreference to CSS phosphor particles coated with a single material, incertain embodiments, it is envisaged that the coatings comprise multiplelayers with combinations of the coating materials described herein.Furthermore, the combination coatings may be coatings with an abrupttransition between the first and second materials, or may be coatings inwhich there is a gradual transition from the first material to thesecond material thus forming a zone with mixed composition that variesthrough the thickness of the coating.

Although the present invention has been described with reference tophosphors for display applications, in embodiments the phosphors of thepresent invention may be used in high CRI (color rendering index) whitelight applications when used in combination with a broad band redemitting phosphor such as Eu²⁺ or Ce³⁺ doped (oxy)nitride compounds, forexample (Ba,Sr)₂Si₅N₈:Eu²⁺ and (Ca,Sr)AlSiN₃:Eu²⁺.

Although the present invention has been particularly described withreference to phosphor compounds in which M is one or more alkaline earthmetals, in embodiments some amount of other metals such as zinc, lithiumor cadmium may substitute for some of the alkaline earth metal.

Although the present invention has been particularly described withreference to coated narrow band red phosphors with general compositionMSe_(1−x)S_(x):Eu, wherein M is at least one of Mg, Ca, Sr, Ba and Znand 0<x<1.0, it is expected that the teaching and principles of thepresent invention will apply more generally to materials of compositionMZ:Eu, wherein M is at least one of Mg, Ca, Sr, Ba, and Z is one or moreof S and Se—for example, (Ca, Sr)S:Eu.

Although the present invention has been particularly described withreference to certain embodiments thereof, it should be readily apparentto those of ordinary skill in the art that changes and modifications inthe form and details may be made without departing from the spirit andscope of the invention.

What is claimed is:
 1. A coated phosphor comprising: phosphor particlesof composition MSe_(1−x)S_(x): Eu, wherein M is at least one of Mg, Ca,Sr, Ba and Zn and 0<x<1.0 having a moisture resistant coating of anoxide material on individual ones of said phosphor particles; whereinthe coated phosphor is configured to satisfy at least one of theconditions: (1) a reduction in relative intensity after 1,000 hours at85° C. and 85% relative humidity is no greater than 15%; (2) a reductionin relative intensity after 1,000 hours at 85° C. and 85% relativehumidity is no greater than 10%; (3) a change in chromaticity coordinateCIE(x) after 1,000 hours at 85° C. and 85% relative humidity is nogreater than 10×10⁻³; (4) a change in chromaticity coordinate CIE(x)after 1,000 hours at 85° C. and 85% relative humidity is no greater than5×10⁻³; (5) said coated phosphor does not turn black when suspended in a1 mol/L silver nitrate solution for at least 2 hours at 85° C.; (6) saidcoated phosphor does not turn black when suspended in a 1 mol/L silvernitrate solution for at least 5 days at 20° C.; and (7) said coatedphosphor is configured such that said coated phosphor does not turnblack when suspended in a 1 mol/L silver nitrate solution for at least30 days at 20° C.
 2. The coated phosphor of claim 1, wherein said oxideis at least one of: alumina, silicon oxide, titanium oxide, zinc oxide,magnesium oxide, zirconium oxide and chromium oxide.
 3. The coatedphosphor of claim 1, wherein said coating has a thickness from 100 nm to5 μm.
 4. The coated phosphor of claim 1, wherein said phosphor particleshave a diameter from 5 μm to 20 μm.
 5. The coated phosphor of claim 1,wherein M is at least Ca.
 6. The coated phosphor of claim 5, whereinsaid coated phosphor has a peak photoluminescence emission wavelengthfrom 600 nm to 650 nm and a FWHM from 48 nm to 60 nm.
 7. A white lightemitting device comprising: an excitation source with emissionwavelength from 200 nm to 480 nm; a first phosphor of compositionMSe_(1−x)S_(x): Eu in which M is at least one of Mg, Ca, Sr, Ba and Znand 0<x<1.0, wherein said first phosphor has a moisture resistantcoating of an oxide on individual particles of said first phosphor andhas a first peak emission wavelength; and a second phosphor with asecond peak emission wavelength different to said firstphotoluminescence peak wavelength.
 8. The white light emitting device ofclaim 7, wherein said first peak emission wavelength is from about 600nm to about 650 nm; and said second peak emission wavelength is fromabout 515 nm to about 570 nm.
 9. The white light emitting device ofclaim 7, wherein the device has a lumen efficacy of at least 335 lm/W.10. A white light emission device for backlighting, comprising: anexcitation source with an emission wavelength from 440 nm to 480 nm; afirst phosphor of composition MSe_(1−x)S_(x): Eu in which M is at leastone of Mg, Ca, Sr, Ba and Zn and 0<x<1.0, wherein said first phosphorhas a moisture resistant coating of oxide on individual particles ofsaid first phosphor and has a peak emission wavelength from 625 nm to645 nm; and a second phosphor with a peak emission wavelength from 520nm to 545 nm; wherein said backlight generates light with a color gamutof at least 85% of NTSC.
 11. The backlight white light emission devicefor backlighting of claim 2, wherein said backlight generates light witha color gamut of at least 90% up to 93% of NTSC.
 12. The backlight whitelight emission device for backlighting of claim 2, wherein said secondphosphor comprises one of β-SiAlON :Eu and SrGa₂S₄:Eu.